The use of gel electrophoresis is currently the ubiquitous technique for the separation of biological materials. Nonbiological materials can also be separated using gels or other chromatographic supports as well, but the scope of effort with regard to biologicals is greater. Typical applications include separation of nucleic acid fragments of various sizes either in the context of sequence determination; in the detection of polymorphisms; or verification of sizes in other contexts. Also frequently conducted are separations of proteins, glycoproteins, protein fragments and application of gel separations as verification of homogeneity or purity, identification of post translational modifications and confirmation of molecular weight.
In all of these procedures, mixed samples of biological entities are applied to electrophoretic gels and the components are separated by application of an electric field across the gel. Regardless of the manner in which the gel is developed, the resulting pattern of migration of the substances contained in the sample must be detected in some manner.
To conduct this detection, typically the gel support is contacted with a blotting membrane to which the substances are transferred in the same pattern in which they appeared on the gel. The “spots” are then detected, at a minimum, by blocking the membrane with a protein or detergent solution to reduce non-specific binding (which otherwise leads to a high level of noise and low level of detection). Typical blocking agents include casein, bovine serum albumin (BSA), non-fat dry milk (generally about 1-5%) in a Tris buffer saline solution with TWEEN® surfactant (TBS-T solution) or phosphate buffer saline solution with TWEEN® surfactant (PBS-T solution). The biological entity is then incubated with an antibody specific for the antigen on the membrane. The membrane is then extensively washed to remove any contaminants, unbound blocking proteins or antibodies and the like. The membrane is then treated and incubated with a secondary enzyme-, radioisotope-, fluorfluor-, or biotin-conjugated antibody specific for the primary antibody. The membrane is then extensively washed again to remove any unbound secondary antibody. Then a detection reagent, generally a chromogenic, chemiluminescent, fluorescent, radiological, or streptavidin-labeled material, is applied which either binds to, or is a substrate of the enzyme-conjugate. Lastly, the appropriate detection device is used to determine the presence, absence, position, quantity, etc. of the biological entity. The last six steps generally take from 3-6 hours to overnight depending on the speed of the reaction between the selected reagents, the membrane and the biological entity. The process requires multiple incubation periods of the membrane on a rocking or other suitable mixing platform. It is a lengthy process that most researchers dislike and which consumes (wastes) a large volume of reagents.
Some researchers have suggested the use of the capillary action of an absorbent material such as filter paper placed below the membrane to draw the remaining fluids through the membrane and improve the speed of the process especially the washing steps.
U.S. Pat. No. 5,155,049 mentions a system called the Hybrid-Ease™ hybridization chamber marketed by Hoefer Scientific Instruments. This chamber is comprised two grids between which the membrane is sandwiched. The grid plates are snapped into position surrounding the membrane, and syringes fitted into the open space created by the grids. One syringe is used to apply reagents and wash, and the other to withdraw excess. The system requires large volumes of liquid in order to operate, is cumbersome to employ and is still quite time consuming. It also mentions that in some particular assays, such as ELISA assays, in small volume wells (such as 96 well microtiter plate), others have used vacuum to draw liquids through a membrane in a washing step. However, they discount this effort as it is only available in small volume applications and still is uncontrollable. They suggest instead that the better method is to use a manual press having the membrane on top of a filter paper and cover layer and then pressing the membrane sandwich between two plates to squeeze the liquid through the membrane and into the paper.
In U.S. Ser. No. 60/732,994, filed Nov. 3, 2005 it is suggested that one use a device formed of several layers including a porous support layer below the one or more layers of blotting membrane, a flow distributor above the blotting membrane(s) and a well on the flow distributor to contain the liquid to the desired area and to allow for lower starting volumes of such liquid. Preferably, the flow distributor is a non-binding or low binding porous membrane such as a 0.22 micron membrane. The device layers are assembled in order and then subjected to vacuum or pressure filtration to wash and detect the biological entities on the membrane.
It is clear that a more efficient method for detection of the biological materials or entities on blotting membranes is required. The present invention permits a more effective and efficient detection of biological entities in a blotting membrane.